The present invention relates to new organopolysiloxanes which contain acyl thiourea groups and which can be used to remove noble and base metals from diluted aqueous or organic solutions. In addition, the present invention relates to methods of preparing these new organopolysiloxanes.
The removal and separation of metals from aqueous or organic solutions, which are frequently present in very diluted form, constitutes a significant problem in many areas of industry. This is due in part to completely different points of view. One aspect can be, for example, the recovery of valuable noble metals from catalytic or developmental processes. Another viewpoint is the purification e.g. of solutions, of drinking water or for waste water for reasons of toxicology or of environmental protection.
The various reasons why the separation of metals from solutions is of interest can also be seen from the following literature cited by way of example:
DE-OS No. 33 47 406; DD Pat. Nos. 207 915; 212 190; 212 257; U.S. Pat. No. 4,448,694; DE-OS No. 25 22 812; DE Pat. Nos. 33 40 055; 33 40 056; EP-OS No. 0 030 106; U.S. Pat. No. 4,377,555; DE-OS No. 30 02 883 or U.S. Pat. No. 3,978,148.
Various methods are used to separate these metals from their solutions. It is frequently customary to use suitably modified organic polymers (e.g. DD Pat. Nos. 207 915; 212 190; 212 257 or U.S. Pat. No. 4,448,694) or to use liquid or dissolved complex-formation agents (cf. DE Pat. Nos. 33 40 055 and 33 40 056; DE-OS No. 33 47 406). However, these methods are not ideal. On the one hand, the organic polymer carriers used are frequently not equal to the requirements, due to their low temperature and solvent stability. On the other hand, the use of liquid or dissolved complexing agents requires a technical expense which can be considerable in some instances.
Basically, it would be more advantageous to use suitably functionalized inorganic carriers such as e.g. silica gel, which exhibit in particular a better temperature and solvent stability. Such systems have also already been prepared and employed (cf. GB No. 1,532,295); however, they have the disadvantage that these inorganic carriers can be functionalized only to a relatively limited extent.
It is therefore an object of the present invention to provide a method for the preparation of metal adsorbent systems based on a polymer framework of primarily inorganic character and to avoid at the same time the above-mentioned disadvantage of a too-low metal ion binding capacity.
It also appeared to be especially suitable to use an acyl thiourea group as complexing unit which has proven to be especially effective (cf. DE Pat. Nos. 33 40 055 and 33 40 056 or DD-PS No. 212 190).